Clinical laboratory tests provide physicians and other healthcare workers with critical information to aid in the diagnosis and prognosis of medical conditions. The importance of clinical laboratory tests is underscored by the fact that over 70% of healthcare decisions are based upon these tests. Many, if not most, clinical laboratory tests rely on safe, quick, reliable, and repeatable collection, transportation, and analysis of blood samples.
Typically, blood samples are collected by trained phlebotomists who draw blood into a tube connected to a needle that is inserted into a donor's vein. Many individuals are fearful or uncomfortable with this method of blood collection. Also, the need for a trained phlebotomist to collect the sample limits the number of locations where samples can be collected, often resulting in much inconvenience for the donor, and adds labor costs to the overall collection process.
If the sample is intended for analysis at a distant laboratory, various protocols must be observed in preparing and sending a shipment of the sample to ensure the integrity of the sample, identity of the sample, and safety of individuals who may come into contact with the shipment. Samples are usually placed in a refrigerated shipping container and transported to laboratories through an expedited shipping method. These steps add considerable costs to the testing process. The stability of certain target analytes during the transport process is also of concern.
Given the expenses and analytical variables associated with the conventional process of collecting, transporting, and analyzing blood samples, along with the drawbacks this process imposes on sample donors, alternative approaches have been actively pursued. One such approach focuses on expanding the use of dried blood spot (DBS) methods. With DBS, small blood samples, usually obtained from a finger or heel prick, are spotted and dried onto specialized filter paper. The dried samples can then be shipped to a laboratory through the mail without the need for refrigeration.
Although DBS sampling provides certain advantages over conventional syringe blood collections, the technology also has a number of drawbacks that severely limit its utility.
Once a DBS sample has reached the laboratory, analytes must be recovered through an extraction process which involves punching out an area of sample-containing filter paper for analysis. Typically, a circular disc with a 3-6 mm diameter is punched out with an instrument that must come into direct contact with the sample-containing filter, potentially contaminating the instrument, and requiring that the instrument be decontaminated between sample punches. This procedure also requires considerably more blood to be collected than is actually used in the analysis.
Another problem with the DBS method is its inability to provide a precisely defined volume of sample to assay, due to the inherent variability of sample hematocrit values (the percentage of blood volume comprised of red blood cells). This problem, sometimes referred to as “hematocrit bias”, occurs because red blood cells affect sample viscosity (viscosity increases in proportion to red blood cell concentration) and viscosity in turn affects the amount of area covered by a blood sample on a piece of collection paper (for a given volume of blood, less viscous samples will spread out over a larger area of collection paper). Standard laboratory procedures usually calculate volume based on the average hematocrit level for a given population, resulting in a considerable underestimation or overestimation for those samples that have hematocrit values considerably different from the mean. This presumptive step can proportionately bias the value of the test result, in some cases resulting in miscalculations greater than 20%.
Another problem with the DBS method is the tendency for certain analytes in a sample to become heterogeneously distributed through the paper matrix due to chromatographic effects of the paper. This can lead to inaccurate results as areas of the paper collected for sampling may have variably lower or higher concentrations of the target analyte.
Still another problem with the DBS method has to do with variability in analyte recovery during the extraction process. Conventional DBS methods provide no practical approach for monitoring the efficiency of analyte recovery which can lead to significant underestimation of analyte concentration.
While the DBS method does not require a phlebotomist to collect the sample, there are critical steps in the procedure that, if not performed properly, can lead to erroneous test results. For example, touching the filter paper or applying too small a volume can lead to variations in sample volume per unit area. While proper spotting technique may mitigate this variability, the technique itself is often difficult for donors to appropriately master. The donor must create a hanging drop that is sufficiently large, but not so large that it accidentally drips from the finger (which can cause splattering and contamination). The drop must then be applied to the filter paper in such a way that inadvertently causes the finger to obscure from view the contact point between the blood sample and paper, contributing to the possibility that the donor will accidentally touch the paper or apply an insufficient amount of sample.
Thus, there remains a compelling need to develop test systems and methods that can incorporate dried blood samples in a way that solves the problems that exist with all current approaches.
The present invention provides a simple and easy-to-use means for collecting and drying a sample of blood, transporting the dried blood to a laboratory, and analyzing the dried blood sample with a level of accuracy, consistency, and reliability not achievable with current approaches. In particular, the present invention provides a collection procedure considerably more user-friendly than the standard DBS procedure and resolves the problematic DBS issues regarding hematocrit bias, chromatographic effects, and variable extraction recoveries.